1. Field of the Invention
The field of the invention is machines used in agriculture which lay down plastic films covering seed beds of soil under which are planted agricultural crops with the stems of the crop protruding upward through openings in the plastic film.
2. Description of the Related Art
In agriculture, it has become common practice to place a thin flexible plastic film or sheet on the ground overlaying elongated seed beds wherein the planted crop has its stems protruding through an opening in the plastic. With this practice, the ground surrounding the base of the plant stem from which the roots grow is covered with the plastic sheet. The plastic sheet may be opaque, thereby denying sunlight to surrounding weeds so that they will not flourish, or the plastic may be clear, in which case the weeds cannot push up through the plastic and wither and die. In addition, a further advantage of laying plastic sheets over crop plants is that water evaporation from the soil is prevented, leaving the water entrapped in the soil for the benefit of the plant itself.
Now tractor pulled machines have been devised and are in common use laying an elongated plastic sheet or film upon long rows of seed beds. These seed beds are formed by furrows cut in the soil on either side of the seed bed, which provide conduits for irrigation water. The common practice in laying down the plastic film on the seed bed is to play it out from a roll with the longitudinal side edges of the film extending down into the oppositely situated furrows and momentarily held there by rolling wheels (hold down wheels) pressing down upon the plastic film. Immediately behind each pressing wheel is a covering disc which takes soil from the furrow and throws it upon the longitudinal side edges of the plastic sheet. This soil thrown up and onto the sides of the plastic sheet anchor it in place. It is anticipated that the plastic film will reside over the seed bed for a considerable period of time, hopefully until the crop is harvested.
It is obvious from the above description that the plastic film needs to be as wide as a seed bed plus the slanted side of each furrow on each side of the seed bed and the trough of the furrow. Now since water is directed to the crops by irrigation methods of running the water into the furrows, the sheet of plastic may be no wider than a seed bed (together with 1 side wall and bottom of each oppositely situated furrow) unless measures are taken to cut the plastic sheet at the bottom of the furrow, or to make perforations through it at that point. It is necessary for the irrigation water in the furrow to seep into the ground and if the plastic sheet is continuous in lining the furrow, no water will penetrate. In many cases, the plastic sheet may be from 2 to 4 or 5 feet in width depending upon the seed bed. The seed beds may vary in length from a few hundred feet to thousands of feet so it is obvious that rather large rolls of plastic film are utilized.
A number of United States patents have been issued pertaining to tractor pulled devices applying and securing a plastic film onto a seed bed, for example, Emily in U.S. Pat. No. 4,953,482 discloses a film laying machine which accomplishes the purposes outlined above and, in addition, includes a cutter which severs the plastic film at the end of a row. Further, the machine provides means for covering the severed ends. Hoeft in U.S. Pat. No. 4,888,913 similarly describes a plastic film laying machine employing a transmission system with a variable speed drive in order to accommodate the different tension forces exerted on the plastic film when it is laid across uneven seed beds. Pavan in U.S. Pat. No. 4,117,787 similarly discloses such a film laying machine wherein the machine perforates the plastic sheet for plant locations prior to laying the sheet upon the ground. Leavitt in U.S. Pat. No. 3,945,330 also provides a plastic film laying machine wherein a transmission synchronizes perforations in the film to align with seeds deposited in the ground.
Lastly, in two earlier patents, namely U.S. Pat. Nos. 3,468,267 to Morris and 3,315,623 to Tschudy, early models of plastic film laying machines are shown and described, incorporating the method of operation initially discussed.
All of the above machines appear to perform their functions satisfactorily, however, it has been the inventor's experience that present available film laying machines suffer from shortcomings in that in the presence of winds having speeds above minimal levels, the wind picks up the plastic film before it can be held down by the pressing wheels or the wind may even pick it up before it can be covered with soil by the closing discs along the longitudinal side edges of the plastic film. As a consequence, the inventor has experienced many occasions where plastic film laying must come to a halt because of blowing winds, resuming only after the winds have died down or ceased. With present film laying machines, winds over 5 to 7 mph appear to adversely affect operations.
In an effort to somewhat counter the effects of winds, the manufacturers of the film laying machines recommend utilizing plastic sheet with increased thickness so as to make the sheet less susceptible to disturbing winds.
The use of spring-laden or floating, hold-down wheels under some circumstances is satisfactory and sufficient for retaining the plastic film on the bed until covering discs secure it. However, soil preparation (clods of soil) and irregularities of the beds often change bed contour and result in abnormal stresses on the plastic film as a consequence of constant and specific points of pressure caused by hold-down wheels. The wheels tend to bounce and their bouncing increases with speed and irregularities that often have to be compensated by reduced speed or an additional operator.
It is thus readily apparent that there is need for improvements to film laying machines which allow the machines to continue working in spite of and even during the winds and/or abnormal soil and bed preparation conditions. Also obviously, it would be of great advantage if improvements to the present available plastic film laying machines were available such that thinner (and obviously much cheaper) plastic films could be utilized at higher speeds.